Image and/or audio data taken by a digital camera would conventionally be recorded onto a recording device provided in the camera, such as a flash memory, or onto a recording medium freely removable from the camera. Also, a system has been devised and introduced commercially which connects a digital camera with an information processing apparatus such as a computer (referred to as PC hereinafter) through a cable or the like thereby to transfer to the PC information of image data recorded onto a recording device in the digital camera or onto a recording medium removable from the digital camera.
Upon such data transfer, commonly used protocols are a Picture Transfer Protocol (PTP) which is a standard data transfer protocol tailored to digital cameras, and Mass Storage Class (MSC) which is a so-called removable disk-related protocol. When the MSC is used for connecting the digital camera with the PC, the digital camera is handled simply as an external recording device such as an externally connected hard disk drive (HDD) or a card reader. This allows users to easily access image data in the camera without any particular driver software or technical knowledge.
The use of the MSC, however, causes the PC to control all file accesses, and is therefore unsuitable for a system which permits concurrent operations of manipulating the camera with operation members provided thereon and of accessing the camera from the PC. In the camera, Read and Write commands are merely executed according to a designated address and length of data and it is difficult to manage data in meaningful units such as files.
Furthermore, except for users who have detailed knowledge of the PC, many digital camera users, which have been increasing recently, are not familiar with the PC. Such users may have difficulty in identifying the digital camera due to the MSC because the camera is recognized simply as an external storage device on an operation system, so that those users probably get confused.
On the other hand, when the PTP is used for connecting the digital camera to the PC, it is easy for users to identify the digital camera because, unlike the MSC, the camera is handled not simply as a storage device but as a digital camera on an operating system, and thus operability can be more improved. Also, the PTP is designed for digital cameras, thereby allowing the camera to manage object data by defining data of files as objects.
Moreover, recently developed operating systems, Windows® XP and MacOSX®, come with a PTP compliant driver from the OS vender so that special driver software is not necessary when connected to the digital camera.
Also, when the PTP is used, the camera manages data by the object as is described above, and thus it is possible to, relatively more easily than the MSC, configure a system capable of concurrent operations to both the camera and PC. Additionally, it is convenient for users since they can identify the digital camera.
The PTP, however, possesses the following disadvantage. It is assumed in the PTP that a system is to be configured so that, when the camera is connected to the PC, the camera itself generates attribute information of all object data stored in the camera and PC acquires those attribute information. Therefore, large amount of image data in the camera requires substantial amount of time to be acquired by the PC when the camera is connected thereto, and users thus have to wait long without moving on to the subsequent operations.